In circuit design, due to the change of market requirements, when the function needs to be expanded, an expansion module is usually added on the basis of the original circuit. The expansion module includes a data circuit, a wireless radiofrequency circuit, and other modules. At the moment, the original circuit is a host module, and the expanded module is an accessory module.
However, since a digital circuit module in a circuit of the expansion module forms a loop itself, a noise problem is easily caused in the long-line transmission or the digital-analog hybrid use of a single-ended analogue signal (the single-ended analogue signal is an analogue signal forming a loop with the ground), which will greatly interfere the ground and a power supply, thus resulting in the imbalance between a ground potential of the host module and a ground potential of the accessory module. It is equivalent to that the ground wire of the accessory module has a potential difference relative to the ground of the host module, and the potential difference can be deemed as noises. The reference potential of the original signal line is the ground wire of the host module, and when it is connected to the accessory module, it is subject to the ground wire of the accessory module. The signal line connected to the accessory module is no longer the original signal relative to the ground wire of the host module, but is superimposed with the noises of the accessory ground, and the noises are also amplified after the amplification processing, which affects the signal quality. The situation where the analogue signal line is interfered is especially apparent, and the signal is attenuated.
The current solutions are usually as follows: (1) filtering the analogue signal in the accessory module, and increasing the filtering by grounding capacitance; and (2) processing a power supply signal and a digital signal, such as isolation and filtering.
However, the current solutions have the following shortcomings: for the solution (1), it is relatively difficult to select the filtering capacitance. when the capacitance is too little, it is noneffective, and if the capacitance is too large, the signal will be affected; and for the solution (2), additional resource input is needed, and a circuit board needs to be enlarged, which has a relatively high cost.